CVT Efficiency

[oilburner]

Anyone know the efficiency of CVTs, particularly the Comet units that seem to be popular for diesel convesions?

In 1995 Ed Otto, who rode a Honda Helix (CN250) in the Iron Butt rally, dynoed his Helix - it put put 13.2hp at the rear wheel. The Helix has 17 hp which, according to my calculator, translates into a 22 percent drivetrain loss. The Honda CVT ratios are 1.8:1 to 1.6:1 via gearing in the rear wheel. The belt runs continuously with the centrifugal clutch also in the rear wheel. The continuous running of the belt results in extended belt life - my belts are well within spec after 24,000 miles.

Perhaps a CVT isn't a good choice for a 10 hp diesel?

FYI

Avery

[balboa_71]

Avery,
Used to own a CH250 Honda with same belt set up....worked great, better than the Comet system. I'd do it again if I could....great bike. As you know, all tranny's lose power, and right angle drive (drive shaft bikes) are even worse due to friction at 90° joint(s). Some bikes have one joint (BMW), and some have two (Japanese in line four engines with shaft drive, Suzi GS series as example). Anyway, for some of us (in US), CVT is still the best way to go due to expense if finding and using a gear box.

Cris

[LocomotiveBreath]

Avery,

I'm sold on a CVT hands down. My set up is reported as I believe company standards are right in the 92% efficiency range. That's only an 8% loss. On the 17HP Helix, did you have any means to accurately check if there were 17hp at the flywheel or just taken what was advertised? Any drag in the brakes (disc?), wheel bearings? Was it in tune? Altitude? Wore out high milage, new and not broken in? Tire pressure? Type of fuel? Lots of other factors need to be looked at before you come up with your conclusions. I'm pretty sure Honda knows what they are doing. Torque curve is very different from a 250cc gas engine vs. a 250cc Diesel, and the 10hp Diesels are in the 400-435cc range, lots more torque.

As for your reported gearing range on the Helix, the 1190 set up I’m going to use has a 3.5:1 Low and feathers to 0.68:1 overdrive. How many gears would you need in your BMW Transmission to keep your D950 within a 2200-2800rpm ideal power band per gear selection to cover the same spectrum? I see you like to play with formulas, how many? When you do that, I'm thinking your gears are all helical cut causing more drag from side thrust. What kind of power loss would you have to have a Transmission with the 13-20 speeds you might need? My CVT will be/is set up to maintain my D954T at an ideal 2400rpm, then let the CVT do it's thing. http://tinyurl.com/y3krt4

As for your statement, how many 4,6,&10hp engines do just fine with CVT, anytime someone sticks a manual transmission which have gear splits set up for gas engines, shoot themselves if the foot for performance, either top end, acceleration or gear splits so far as they have to wind the engine out to max rpm just to shift and have engine lug in the next gear. I know, I hate my 3rd-4th gear split. I grew up with 5-8 hp Briggs Tote Goats and with old technology, they still performed very well. http://users.infoconex.com/~ramrod/gallery.htm
Note, the blue Tote Goat with a CVT and shaft drive! No new technology, Tote Goats were simple, easy to work on and dependable.

You did a nice job on your bell housing (how many zillion hours of work?) You’re looking for special gears being made by someone in some far away land to get your bike into a respectable speed. When if you just go to a CVT you could have your cake and eat it too. Notice in the picture the factory B&S bell housing: http://img232.imageshack.us/img232/2236/dscf0007od5.jpg

From my scattered memory (I like to smoke pot) we have had this conversation before in another forum. Stop discouraging those that question the use of a CVT over the complicated adaption of a manual transmission, clutch, primary drive and the headache that follows. The only transmissions here in the States are way to overpriced Harley's. But we are all different, if you want a manual tranny, then head on.


Any questions?

Dave

[oilburner]

One question. What is your *overall* gearing? Your CVT provides 3.5:1 to 0.68:1, and I would guess you will be using a conventional chain and sprocket setup from the CVT to the rear wheel? What will be the ratio of the chain sprockets?

Thanks

Avery

[LocomotiveBreath]

I've purchased several Honda GL1800 one side swingarms and final drives that offer both 2.86:1 or 2.75:1. The ones I've purchased have the 2.75:1, this giving me an approx. 137.454 mph @ 3600 rpm with a 24" diameter tire @ the highest ratio. I'll run out of power before I reach that speed. http://www.angelfire.com/fl/procrastination/rear.html I've also machined up several sets of swingarm mounting bosses with the correct thread for the stock GL1800 mounting pins, (for sale @ $129 a pair) as I see the use of this swingarm has many custom applications with the 5x100mm wheel bolt pattern. http://tinyurl.com/w77lh Also the Honda brake assembly has a 316mm vented disc brake, a caliper which has twin brake ports so you can tie in the front brakes (one piston). Anti lock brake sensors for those that have the electronic talent that I don't have

Dave

[oilburner]

Hi Dave;

I've got a couple more questions.

First of all, several comments.

I think the discussion of the various approaches to gearing e.g. CVT, gearbox etc. are beneficial for those currently considering a project. As they say, different strokes for different folks.

1)For the record I much prefer a CVT over a gearbox, but my design objectives for the current project rule out a CVT. Maybe next time...

2)If the standard BMW gearbox proves to be inadequate i.e. engine is capable of taller gearing while maintaining good performance at normal speeds, I have a specially modified BMW gearbox (1:1 in top gear) and five different BMW final drives (2.91, 3.09, 3.20, 3.36, 3.56) to fine tune the setup for up to a theoretical 95.6 mph @ 3600 rpm. According to the hp-mph formula, my D950 will do well to achieve 86 mph at the engine's max of 23.8 hp, so I don't anticipate a problem with insufficient gearing.

3)The 954DT turboed engine has 40 percent more torque (continuous) and 41 percent more horsepower (continuous) at 2400 rpm compared to my normally aspirated D950 engine; according to the hp-mph formula it should be capable of approximately 94.2 mph before it runs out of power, and another of my favourite formulas indicates the 954DT should cruise comfortably around 80 mph @ 2400 rpm. My D950 *might* be capable of a 70 mph cruise at 2400 rpm but I somehow doubt it. (See next comment).

4) I installed my modified BMW gearbox into a 750cc BMW. The engine was in excellent running condition and the bike pulled strongly with its stock gearbox and final drive and performance was on par with any of the other numerous 750cc-800cc BMWs I have owned and maintained over the past 26 years. With the modified gearbox, at 84 mph, I shifted into top gear and the engine could not sustain 84 mph on level road with no wind while producing a maximum of 38.7 ft. lbs of torque and 26hp at 3500 rpm as per BMW hp & torque graphs. This experience figures significantly as a baseline for performance expectations of my project.

Questions.

(1) Are you installing your engine with the crankshaft north-south as on the GoldWing? If so, what is the CVT pulley orientation (e.g. one over the other) and how will it be connected to the driveshaft?

(2) How does your CVT provide the equivalent of dropping down a gear for passing?


It will be interesting to get a few more of these bikes on the road and get some real world performance numbers.

The following is an interesting tidbit I found on the internet that puts torque and horsepower into perspective:

<start of excerpt>
... a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a couple of hundred years ago), rotating lazily on a shaft which was connected to the works inside a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically generated about 2600(!) foot pounds of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If we hooked that wheel to, say, the drivewheels of a car, that car would go from zero to twelve rpm in a flash, and the waterwheel would hardly notice .

On the other hand, twelve rpm of the drivewheels is around one mph for the average car, and, in order to go faster, we'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot pounds of torque at the output, which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60. Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over five thousand two hundred fifty two gives us:

6 HP.

Oops. Now we see the rest of the story. While it's clearly true that the water wheel can exert a *bunch* of force, its *power* (ability to do work over time) is severely limited."

<end of excerpt>

Thanks

BTW Dave nice job of the swingarm mounts.

Avery

[balboa_71]

The only thing I don't like about the Comet set up is the "clutching" method:
Squeezing of the belt for friction to get moving. Hondas setup is way ahead of the game as the belt and pully's are all turning when the engine is running. There is a centrifical clutch that is driven by the "driven" member of the CVT.
Belt and pully faces get little wear, and centrifical clutch takes the beating.
IMHO, this arrangement would be great on one of our bikes, but it isn't going to happen. After time, belts have to be replaced and the drive unit will as well. I don't know if it would be less expensive to rebuild the drive unit???
Perhaps having the drive pully's faces hard anodized might offer additional wear resistance. Drive pully's built out of 7075-T6 and hard anodized would be superior to using mild steel (C1018).

Cris

[balboa_71]

A few years ago I stumbled across a book for sale regarding "tuning" Comet CVT systems. I think it was around $30. Have any of you run across some mention of this publication on the net???

Thanks,
Cris

[LocomotiveBreath]

Avery,

Now we are getting somewhere and thank you for the compliment on the mounts, but thank Dyell Machine Shop in Hesperia. I just drafted what I needed and I had to buy the special tap to cut the threads to mate with the Honda swingarm pivot screws. Thank you also for all your formulas and calculations.

Now, let me toss in another factor to your formulas, our engines are rated and built to deliver a 100% duty cycle. With the larger engines 16hp and more let’s say, we can look at ways to up the HP and Torque with less than the 100% duty cycle. These engines in our application will rarely if ever see 100%. I've talked with Terry Martin (Green Softtal with the D950T) He runs right up to the governor @82mph, but he has never seen the waste gate open, telling me the engine runs up to speed, but does it with ease with boost under 4psi (I think thats what factory settings are) I’ll start watching boost and EGT and little by little I could increase hp if I wanted, i.e. more boost, propane, nitrous with up to if not more than double the power/torque @ a 2-5% duty cycle for short bursts. The Hot Rodder in us. But you’ve answered my question, I should be able to maintain a 65-75mph with little or no problem and NOT be running my engine up to the governor. My days of going fast is over I think (smile).

Remember some of the early Hot Rods were light body Fords w/Chrysler Hemi’s, Chrysler Hemi’s started life as low hp, high torque 100% duty cycle industrial motor. http://www.allpar.com/mopar/hemi/chrysler-hemi.html See where I’m heading? This is my old Hemi Car I owned and restored on the late 70’s-early 80’s. http://www.moparts.org/moparts/carshow/ ... /jimk.html When I see a Hemi, I just think of its just tinny uni-body Plymouth/Dodge with an industrial motor that makes noise, burns rubber, goes no-where fast and eats lot’s of av-gas @4-6mpg. Now these fetch 250K up to 4 million for a 71 Hemi Cuda Convert. I put over 45,000 miles on her, now they just sit in garages and wait as the owners look to find another sucker to buy them at a price more than what they invested in them.


As for your question, I’ll run the engine inline, like yours, my Dnepr, same orientation as the Track bike, or like one of our other fellow diesel bikers shown on the what “Diesel Bike do you ride” section on general chat. I asked Comet and Quality Drive (30 years experience w/Salsbury) the most efficient and ideal pulley centers. I’m running my pulley centers very close @ 10”-10.5”, orientation will be determined when I get the frame started. I can’t seem to find a frame builder to work with me as they all seem you can’t have a bike without a mega dollar HD boat anchor for a propulsion unit. So I have to build my own, which means I have to assemble the tools I lost in my divorce 12 years ago, and at Social Security wages (did I mention I’m disabled? “Mental”) it’s taking some time, I’ll get there.

Passing power? Well with the Rapid Reaction drive pulley, I have both the clutch and pulley tunable, and gave Quality Drive my requirements, and are pre-setup, but if I don’t like the performance, I can change ramps, springs, weights, etc. to my requirements.

As for drive line shock upon startup, the GL1800 Goldwing’s drive shaft is rubber insolated within its construction, also I’m looking into Team Industries ATV driven pulley as it is also designed with shock prevention for this same purpose. But this problem is my least concern. How may Golfers are sueing the golf cart manufactures for whiplash?

Dave